1. Field of the Invention
This invention relates to a polymerization process, and more particularly, to non-aqueous, heterogeneous polymerization of a vinyl amide monomer in oil as a solvent and including a water-soluble cosolvent.
2. Description of the Prior Art
J. Shih, in U.S. Pat. Nos. 6,255,421; 6,255,422 and 6,300,442; described a non-aqueous, heterogeneous polymerization process for making vinyl polymers using an oil solvent, whose presence both during the polymerization and in the reaction product is advantageous for commercial use of the vinyl polymer, particularly in cosmetic compositions.
Accordingly, in this invention, it is desired to provide a new and improved non-aqueous, polymerization process to increase the stability of a polymer/oil-cosolvent solution.
These and other objects and features of the invention will be made apparent from the following description of the invention.
What is described herein is a non-aqueous, heterogeneous polymerization process for making vinyl amide polymers. The process comprises heating a reaction mixture of, by weight, about 5-70%, preferably 10-50% of a vinyl amide monomer in an oil as solvent, and including a water-soluble cosolvent, and a free radical initiator, optionally in the presence of a crosslinking agent and/or a surfactant, wherein the oil solvent is present in an amount sufficient to keep the resultant polymer in a stable stirrable state throughout the polymerization. The polymer reaction product obtained thereby is capable of forming a uniform emulsion or gel upon addition of water thereto.
The unique properties of many oils make it desirable to include them in aqueous-based compositions. For example, cosmetically and pharmaceutically-acceptable materials such as silicone oils, fluids and gums, mineral oils, and water-insoluble organic esters such as isopropyl palmitate and isopropyl myristate, are particularly useful in formulations for the hair and skin. In these compositions, the lubricity and hydrophobicity properties of the oils are beneficial for the user.
In this invention, vinyl polymers useful in cosmetic compositions are prepared in a non-aqueous, heterogeneous polymerization process using both an oil as a solvent and a water-soluble cosolvent, for the monomer during the polymerization reaction. The oil solvent and water-soluble cosolvent also acts as a medium to keep the polymer product in a stirrable state throughout the polymerization. The reaction product is a slurry of the vinyl polymer in oil. If desired, the reaction product may be filtered to provide the vinyl polymer as a powder swollen with oil. Thereafter, the reaction product itself, or the polymer powder swollen with oil and cosolvent, may be homogenized with water to form a uniform liquid emulsion or gel which is directly useful as the cosmetic or pharmaceutical composition.
Generally about 5-70%, preferably 10-50%, by weight, of the vinyl monomer reactant is used in the process, and about 30-95% of the oil and cosolvent is included for the solvent and medium functions in the process.
Suitable oils for use herein include cosmetically or pharmaceutically-acceptable materials, such as silicone oils, fluids and gums, mineral oils and water-insoluble organic esters such as diisopropyl adipate, isopropyl palmitate, isocetyl stearate and isopropyl myristate.
Suitable silicone oils or fluids for use in the invention may be selected from non-volatile silicones, such as polyalkyl siloxanes, polyaryl siloxanes, polyalkylaryl siloxanes and polyether siloxane copolymers; and volatile silicones such as cyclomethicones also may be used.
Non-volatile polyalkylsiloxanes thus include, for example, polydimethylsiloxanes (Dimethicone) with viscosities ranging from about 5 to about 600,000 centistokes (cS) at 25xc2x0 C. These siloxanes are available, for example, from the General Electric Company as the VISCASIL series and from Dow Corning as the Dow Corning 200 products. Their viscosity can be measured by the glass capillary viscometer procedure set forth in Dow Corning Corporate Test Method CTM 0004 issued Jul. 20, 1970. Preferably, the viscosity of these siloxanes selected have a viscosity of about 100 to about 100,000 cS, and most preferably, a viscosity of up to about 15,000 cS.
Suitable non-volatile polyalkylaryl siloxanes include, for example, poly(methylphenyl) siloxanes having viscosities of about 15 to 65 cS at 25xc2x0 C. These siloxanes are available, for example, from the General Electric as SF 1075 methylphenyl fluid or from Dow Corning as 556 Cosmetic Grade Fluid. Additionally, poly(dimethylsiloxane)-(diphenylsiloxane) copolymers having a viscosity in the range of about 10 to 100,000 cS at 25xc2x0 C. are useful.
These and other suitable silicones are disclosed in U.S. Pat. Nos. 2,826,551, 3,964,500 and 4,364,837.
The cosolvent included in the process is a water soluble compound, preferably a glycol, e.g. 2-methyl-2,4-pentanediol, 1,4-hexanediol and 1,6-hexanediol. The function of the cosolvent is to stabilize the polymer/oil emulsion to a level not ordinarily obtained without the cosolvent present.
The polymerization process is carried out with a free radical initiator present in the polymerization reaction mixture. The reaction product thus includes the vinyl polymer corresponding to the vinyl monomer or monomers selected. Suitable free radical initiators are diacetyl peroxide, dibenzoyl peroxide, dilauroyl peroxide, t-butyl peroxypivalate, t-butyl peroctoate, t-amyl peroxypivalate, t-butyl peroxy-2-ethylhexanoate, di-(4-t-butylcyclohexyl) peroxydicarbonate, 2,2xe2x80x2-azo-bis(isobutyronitrile), 2,2xe2x80x2-azo-bis(2,4-dimethylvaleronitrile), or 1,1xe2x80x2-azo-bis(cyanocyclohexane), and mixtures thereof.
A crosslinked vinyl amide polymer may be obtained in the process when the optional crosslinking agent is included in the reaction mixture. Suitably, the crosslinking agent is present in an amount of about 0.1-10 wt. %, preferably 0.3-3%, based on the amount of vinyl monomer present. In the presence of such a crosslinking agent, the vinyl monomer will form the corresponding crosslinked vinyl polymer, which, upon homogenization with water, will provide a uniform liquid gel product.
In the practice of the present invention, the oil and cosolvent is charged into a reactor, under agitation, and in a nitrogen atmosphere, and heated to about 40xc2x0-150xc2x0 C., preferably about 65xc2x0 C. Then the free radical initiator of 0.1-10%, preferably 0.2-5%, is added. Thereafter the vinyl monomer is added continuously over a period of about 1-12 hours, preferably about 3-6 hours. Preferably, the vinyl monomer and optional crosslinking agent are fed into the reactor at a rate such that substantially no free monomer is present during the polymerization.
After polymerization is complete, the polymer is obtained as a slurry in oil and cosolvent. The slurry can be used as is or filtered to remove excess oil and cosolvent where the product consists of solid polymer with significant amount of absorbed oil. Both slurry and filtered polymer are useful in cosmetic and pharmaceutical formulations.
Suitable vinyl amide monomers include, but are not limited to, and N-vinyl lactams, such as N-vinylpyrrolidone, N-vinylcaprolactam; as well as non-ring vinylamides as N-vinylformamide; optionally with one or more comonomers such as vinyl acetate, acrylic acid, methacrylic acid, acrylamide, methacrylamide, an alkyl(meth)acrylate, an alkyl(meth)acrylamide, a hydroxyalkyl(meth)acrylate and a hydroxyalkyl(meth)acrylamide, and a N,N-dialkylamino-alkyl(meth)acrylate wherein alkyl is independently a C1 to C4 alkyl group and N,N-dialkylaminoalkyl methacrylamide (alkyl being as defined before), and their quaternary derivatives; and mixtures thereof.
Suitable crosslinking agents include, but are not limited to, diallylimidazolidone, divinyl ether of diethylene glycol, pentaerythritol triallyl ether (PETE); pentaerythritol triacrylate (PETA); triallyl-1,3,5-triazine-2,4,6-(1H,3H,5H)trione (TATT), ethylene glycol diacrylate, 2,4,6-triallyloxy-1,3,5-triazine; N-vinyl-3-(E)-ethylidene-pyrrolidone (EVP), 1,7-octadiene, 1,9-decadiene, divinyl benzene, methylene-bis(methacrylamide), methylene-bis(acrylamide), N,N-divinylimidazolidone, ethylidene-bis(N-vinyl-pyrrolidone) (EBVP), hexaallyl sucrose, or bis(N,N-acrylamide).
Another optional component of the reaction mixture is a surfactant. The presence of a surfactant will function to effectively stabilize the desired emulsion and gel products. Generally, an oil soluble surfactant is present in the reaction mixture and a water soluble surfactant during the water homogenization, in an amount of about 0.5-10%, preferably 1-5%, based on oil present. Suitable oil soluble surfactants useful for polymerization include, but are not limited to, cetyl dimethicone copolyol (Abil(copyright) EM-90, product of Goldschmidt Chemical Corp.); Span(copyright) 80 (ICI) and Dow Corning 3225 silicone.
The resultant solutions have a solids content of about 5-70%, preferably 10-50%.
The products made herein may be easily converted into emulsions or emulsified hydrogels which contain the polymer (linear or crosslinked) in the aqueous phase.
The oil phase consists of the oil used during polymerization. The emulsions can be a water-in-oil (w/o), oil-in-water (o/w), or mixed type (w/o/w). When the polymer is crosslinked, the aqueous phase has attributes of a swollen crosslinked hydrogel. The hydrogel phase can be either dispersed in oil as fine gel particles (w/o), or the oil droplets can be dispersed in a continuous hydrogel phase (o/w).
The selected ratios of oil-to-water in such emulsions and emulsified hydrogels are predetermined by the desired use compositions; these can be adjusted within a broad range. Typically, oil-to-water ratios reside in the range of about 30:70 to about 10:90 by volume in the case of o/w emulsions and emulsified hydrogels. In corresponding w/o systems, the ratios of oil-to-water are suitably in the range of about 90:10 to about 30:70 by volume. Typically, when there is a need for a significant amount of oil in the final emulsion, the reaction product, that is, the slurry of polymer in oil, is directly converted into an emulsion or an emulsified hydrogel by addition of a calculated amount of water. When, however, the ratio of oil-to-water in the emulsion is desired to be low, the emulsion is made using the filtered reaction product that consists of polymer powder swollen with the absorbed oil.
When an o/w system is desired, the reaction product is gradually added to water, whereas when a w/o system is desired, water is added gradually to the reaction product, with appropriate rapid agitation or homogenization. Suitable surfactants should be added to these systems, such as, for example, Tween(copyright) 20, 21, 40, 61 (ICI) or Igepal(copyright) CO-630 (product of Rhone-Poulenc), for o/w emulsions and emulsified hydrogels; and Span(copyright) 60, 65, 80, 85 (ICI) for w/o systems. The surfactant added optionally to the polymerization reaction mixture also may be sufficient to form the desired emulsion or emulsified hydrogel.